WASHINGTON (Reuters) - Scientists have figured out how mice
can regain some ability to walk after spinal cord injuries, and
hope this insight can lead to a new approach to restoring
function in people paralyzed by similar damage.

The research, published on Sunday in the journal Nature
Medicine, showed that the brain and spinal cord are able to
reorganize functions after a spinal cord injury to restore
communication at the cellular level needed for walking.

Mice given partial spinal cord injuries in the laboratory
gradually were able over a period of about eight to 10 weeks to
regain the ability to walk, although not as well as before the
injury, according to the scientists.

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After this partial spinal cord injury, the brain and spinal
cord underwent a sort of spontaneous rewiring to control
walking even in the absence of the long, direct nerve highways
that normally connect the brain to the walking center in the
lower spinal cord, the researchers said.

"This is not the end of a story. This is the beginning of a
story," said Dr. Michael Sofroniew, a professor of neurobiology
at the David Geffen School of Medicine at the University of
California at Los Angeles who led the research.

"We have identified what appears to be a previously
unrecognized mechanism for recovery of function after these
kinds of injuries. And we need to understand it better and
learn how to exploit it better, through doing the right kind of
rehab training and through figuring out ways to stimulate this
kind of recovery," Sofroniew added in a telephone interview.

The spinal cord passes through the neck and back and
contains nerves that transport messages between the brain and
the rest of the body. A spinal cord injury -- from a car
accident, for example -- can cause paralysis below the site of
the injury. There is no cure for such paralysis, and many
scientists have been frustrated by their failure to find one.

SPINAL CORD DAMAGE

Spinal cord damage obstructs the pathways the brain uses to
transit messages to the nerve cells that control walking.
Experts had thought the only way someone with such an injury
could walk again was to somehow regrow the long nerve highways
linking the brain and base of the spinal cord.

But what they found in this study was that when spinal cord
damage blocked direct signals from the brain, the messages were
able to make detours around the injury. Rather than using the
long nerve highways, the message would be transmitted over a
series of shorter connections to deliver the brain's command to
move the legs, the researchers said.

Sofroniew used a traffic analogy. "If you have a big
freeway going somewhere, then that's the fastest route to take.
If that gets blocked and you can't get through, an alternative
way might be simply to get off the freeway and use shorter
interconnected side streets to get around," Sofroniew said.

The researchers blocked half the long nerve fibers on each
side of the spinal cord but did not disturb its center, which
has a connected series of shorter nerve pathways that convey
information over short distances up and down the spinal cord.

The researchers then blocked the short nerve pathways in
the center of the spinal cord, which caused paralysis to
return. This confirmed the nervous system had rerouted messages
from the brain to spinal cord using these shorter pathways.

The researchers said they now hope to figure out how to
encourage nerve cells in the spinal cord to grow and form new
pathways that connect across or around an injury, permitting
the brain to direct these cells and avert paralysis.